Such a function can be easily constructed out of an orthogonal
wavelet mask [1]}. We define a kernel
\(L_{2n}(\cdot ,\cdot )\)  as the following
\(L_{2n}(x,y):=\sum _{k=0}^\infty \eta \left(\frac{k}{n}\right)v_k^2\int _{\mathbf {S}^{d-1}}U_k(x\cdot \xi )U_k(y\cdot \xi )d\omega (\xi ).\) 
